When soldering electronic components on the printed circuit board, the reflow furnace which solders them by fusing solder paste in which solder powder and flux are mixed has been often used in recent years. The reflow furnace contains a preliminary heating zone, a heating zone and a cooling zone within a tunnel muffle. The preliminary heating zone and the heating zone are provide with heaters for heating and the cooling zone is provided with a cooling mechanism being constituted of cooling water pipes, cooling fun or the like.
The reflow furnace is provided with a heated-air-blowing nozzle for blowing the heated air into the muffle. The heated-air-blowing nozzle blows the heated air, which has been heated by the heater, from the nozzle for blowing the heated air into the heating zone in the reflow furnace by the fun(s) driven by a motor. Thus, the heated-air-blowing nozzle forces the heated air to enter any shadow portion by the electronic component(s) and/or any small gap (for example, through-holes) so that the whole printed circuit board can be uniformly heated.
As the heated-air-blowing nozzle provided in the reflow furnace, the nozzles of multi-hole type in which the heated air is blown from the multi-holes have been used. In the nozzles of multi-hole type, a speed of the heated air is faster than that of the nozzle of single-hole type and the multiple holes causes no deficiency of a flow rate of the heated air. Therefore, the nozzles of multi-hole type have excellent heating efficiency. From this, in the reflow furnace, the nozzles of multi-hole type in which the heated air is blown from the multi-holes have been often used.
According to a reflow furnace disclosed in Patent Document 1, multiple heated-air-blowing nozzles are respectively arranged in upper and lower portions of the preliminary heating zone and the heating zone along a conveying direction of the printed circuit board. For example, in the preliminary heating zone constituted of five zones, a total of ten heated-air-blowing nozzles is arranged with every five nozzles being respectively arranged in the upper or lower portion thereof. Further, in a case where the heating zone is constituted of three zones, a total of six heated-air-blowing nozzles is arranged with every three nozzles being respectively arranged in the upper or lower portion thereof. In one reflow furnace, a total of sixteen heated-air-blowing nozzles is arranged with every eight nozzles being respectively arranged in the upper or lower portion thereof.
In the preliminary heating zone, the heating has been normally performed so that the temperature is set to be lower than that of the heating zone or a flow rate of the heated air is set to be smaller. This causes the printed circuit board to be slowly heated so that it is conveyed, without undergoing any heat shook, into the heating zone of the reflow furnace which heats it. In the heating zone, the soldering has been normally performed by heating it so that the temperature is set to be higher than that of the preliminary heating zone or a flow rate of the heated air is set to be larger. Further, the cooling zone has the same basic configuration as those of the preliminary heating zone and the heating zone. However, the heated air, which is heated by the heater(s), blows in the preliminary heating zone and the heating zone while in this cooling zone, the cooling water pipes and the like are provided instead of the heater(s) so that gas contacts the cooling water pipes to be blown to the board as cooled blast, which causes the board to be cooled.
Relating to an arrangement of the blowing nozzles in a heated-air-blowing heater, Patent Document 2 discloses a gas-blowing-hole array structure. In the gas-blowing-hole array structure, a first heated-are-blowing hole and a second heated-are-blowing hole are arranged with a predetermined opening width pitch along a direction that is orthogonal to a conveying direction of the circuit board so that they form a first row. Plural other rows are formed in parallel to the first row along the conveying direction with a row arrangement pitch.
Further, the first heated-air-blowing hole of each of the other rows and the first heated-air-blowing hole of each of the other rows are arranged with a predetermined apace along a width direction. The first heated-air-blowing holes of the first row and other rows are respectively arranged so that they have different phases on the orthogonal direction. Due to this array structure, it is possible to perform any uniform heating by staggering the array along the width direction thereof.